Digital subscriber line (DSL) technologies utilize existing telephone subscriber lines to provide high bandwidth digital communications to end users. Diagram 100 of FIG. 1 provides an illustration of general system. Certain varieties of DSL technology—in particular, asymmetric DSL (ADSL) or Very high rate DSL (VDSL)—are capable of adapting transmission parameters based on channel conditions and end-user demands. ADSL or VDSL technologies utilize a discrete multitone (DMT) line code—one that assigns a number of bits to each tone (or sub-carrier), individually. DMT code may then be adjusted to channel conditions; by determining the number of bits assigned to each tone during training and initialization of modems at each end of a subscriber line.
VDSL2 (ITU-T G.993.2) is an advanced DSL technology that is usually deployed in shorter loops, and uses wider frequency bandwidth when compared with ADSL. Correspondingly, VDSL2 generates a greater degree of crosstalk interference in a line's cable bundle. VDSL2 transceivers on adjacent lines may be seriously affected—especially by far-end crosstalk (FEXT), since such FEXT emanates within those receivers' frequency bands. This is illustrated in reference to diagram 200 of FIG. 2. When an adjacent pair of transceivers starts initialization, an initial pair already in operation suffers from a suddenly increased crosstalk level. VDSL2 crosstalk occurs in a wideband environment. As such, crosstalk is higher at higher frequencies; and crosstalk in VDSL2 is often worse than that in, for example, ADSL. Correspondingly, increments of interference may be much greater than noise margins—causing unacceptable noise margins and bursts of CRC errors that force modems to retrain, which leads to disruptions of service. Such issues are commonly identified in laboratory test and field trials.
In a conventional system, data signals transmitted over twisted-pair phone lines may be significantly degraded by crosstalk interference that is generated on one or more adjacent twisted-pair phone lines in the same (or an adjacent) cable bundle. Correspondingly, suddenly increased crosstalk or other interferences—arising from using twisted-pair phone lines for high data transmission rate technologies (i.e., ADSL or VDSL)—may substantially inhibit proper transmission of data signals.
Therefore, there is a need to provide a system that effectively and efficiently removes or reduces crosstalk interference effects in the operation of high data transmission rate technologies, on an immediate and real-time basis.